Solid Electrolytic Capacitor Containing a Pre-Coat and Intrinsically Conductive Polymer

ABSTRACT

A solid electrolytic capacitor containing a capacitor element is provided. The capacitor element contains an anode body, a dielectric that overlies the anode body, a pre-coat that overlies the dielectric and that is formed from an organometallic compound, and a solid electrolyte that overlies the dielectric. The solid electrolyte includes an intrinsically conductive polymer containing repeating thiophene units of a certain formula.

RELATED APPLICATIONS

The present application claims priority to U.S. Provisional ApplicationSer. No. 62/945,912, filed on Dec. 10, 2019 and 62/947,010, filed onDec. 12, 2019, which are incorporated herein in their entirety byreference thereto.

BACKGROUND OF THE INVENTION

Solid electrolytic capacitors (e.g., tantalum capacitors) are typicallymade by pressing a metal powder (e.g., tantalum) around a metal leadwire, sintering the pressed part, anodizing the sintered anode, andthereafter applying a solid electrolyte. Conductive polymers are oftenemployed as the solid electrolyte due to their advantageous lowequivalent series resistance (“ESR”) and “non-burning/non-ignition”failure mode. For example, such electrolytes can be formed through insitu chemical polymerization of a 3,4-dioxythiophene monomer (“EDOT”) inthe presence of a catalyst and dopant. However, conventional capacitorsthat employ in situ polymerized polymers tend to have a relatively highleakage current (“DCL”) and fail at high voltages, such as experiencedduring a fast switch on or operational current spike. In an attempt toovercome these issues, dispersions have also been employed that areformed from a complex of poly(3,4-ethylenedioxythiophene) andpoly(styrene sulfonic acid (“PEDOT:PSS”). While the PEDOT:PSSdispersions can result in improved leakage current values, otherproblems nevertheless remain. For example, one problem with polymerslurry-based capacitors is that they exhibit relatively poor electricalperformance (e.g., capacitance stability) under certain conditions.

As such, a need exists for an improved solid electrolytic capacitor thatexhibits relatively stable electrical properties.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a solidelectrolytic capacitor is disclosed that contains a capacitor element.The capacitor element contains an anode body, a dielectric that overliesthe anode body, a pre-coat that overlies the dielectric and that isformed from an organometallic compound, and a solid electrolyte thatoverlies the dielectric. The solid electrolyte includes an intrinsicallyconductive polymer containing repeating thiophene units of the followinggeneral formula (I):

wherein,

a is from 0 to 10;

b is from 1 to 18;

R is an optionally substituted C₁-C₆ linear or branched alkyl group or ahalogen atom; and

M is a hydrogen atom, an alkali metal, NH(R¹)₃, or HNC₅H₅, wherein R¹ iseach independently a hydrogen atom or an optionally substituted C₁-C₆alkyl group.

Other features and aspects of the present invention are set forth ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended figures in which:

FIG. 1 is a cross-sectional view of one embodiment of a capacitor of theassembly of the present invention;

FIG. 2 is a cross-sectional view of another embodiment of a capacitor ofthe assembly of the present invention;

FIG. 3 is a cross-sectional view of yet another embodiment of acapacitor of the assembly of the present invention; and

FIG. 4 is a top view of still another embodiment of a capacitor of theassembly of the present invention.

Repeat use of references characters in the present specification anddrawings is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstruction.

Generally speaking, the present invention is directed to a solidelectrolytic capacitor that contains a capacitor element including ananode body, dielectric overlying the anode body, a pre-coat overlyingthe dielectric and formed from an organometallic compound, and a solidelectrolyte overlying the dielectric. To help facilitate the use of thecapacitor in high voltage applications, the solid electrolyte includesan intrinsically conductive polymer containing repeating thiophene unitsof the following general formula (I):

wherein,

a is from 0 to 10;

b is from 1 to 18;

R is an optionally substituted C₁-C₆ linear or branched alkyl group or ahalogen atom; and

M is a hydrogen atom, an alkali metal, NH(R¹)₃, or HNC₅H₅, wherein R¹ iseach independently a hydrogen atom or an optionally substituted C₁-C₆alkyl group.

Without intending to be limited by theory, it is believed that selectivecontrol over the particular nature of the pre-coat and solid electrolytein the manner noted above can help improve certain electrical propertiesof the resulting capacitor. The capacitor may, for example, exhibit arelatively high “breakdown voltage” (voltage at which the capacitorfails), such as about 55 volts or more, in some embodiments about 65volts or more, in some embodiments about 85 volts or more, in someembodiments about 90 volts or more, in some embodiments about 95 voltsor more, and in some embodiments, from about 100 volts to about 300volts, such as determined by increasing the applied voltage inincrements of 3 volts until the leakage current reaches 1 mA. Thecapacitor may also exhibit a high degree of dielectric strength, whichcan improve capacitance stability. The “dielectric strength” generallyrefers to the ratio of the “breakdown voltage” of the capacitor (voltageat which the capacitor fails in volts, “V”) to the thickness of thedielectric (in nanometers, “nm”). The capacitor typically exhibits adielectric strength of about 0.4 V/nm or more, in some embodiments about0.45 V/nm or more, in some embodiments about 0.5 V/nm or more, in someembodiments about 0.6 V/nm or more, in some embodiments about 0.65 V/nmor more, in some embodiments about 0.7 V/nm or more, in some embodimentsfrom about 0.75 to about 1 V/nm, and in some embodiments, from about 0.8to about 0.9 V/nm. While its thickness can generally vary depending onthe particular location of the anode body, the “dielectric thickness”for purposes of determining dielectric strength is generally consideredas the greatest thickness of the dielectric, which typically ranges fromabout 60 to about 500 nm, in some embodiments from about 80 to about 350nm, and in some embodiments, from about 100 to about 300 nm.

The resulting capacitor may be able to maintain stable electricalproperties (e.g., capacitance) under a wide variety of differentconditions. For example, the ratio of the capacitance after beingsubjected to repeated cycles of a surge voltage (“charge-dischargecapacitance”) to the initial capacitance value prior to such testing maybe from about 0.7 to 1, in some embodiments from about 0.8 to 1, in someembodiments from 0.85 to 1, in some embodiments from about 0.9 to 1, insome embodiments from 0.91 to 0.99, and in some embodiments, from 0.92to 0.99. The surge voltage may be applied for 1,000 to 16,000 cycles(e.g., 1,000, 2,000, 3,000, 4,000, 5,000, 8,000, 12,000, or 16,000cycles). After 5,000 cycles, for instance, the capacitor may exhibit acharge-discharge capacitance within the ranges noted above.

In addition, the capacitance may also remain stable even after beingexposed to a high temperature, such as from about 80° C. or more, insome embodiments from about 100° C. to about 150° C., and in someembodiments, from about 105° C. to about 130° C. (e.g., 105° C. or 125°C.) for a substantial period of time, such as for about 100 hours ormore, and in some embodiments, from about 150 hours to about 3,000 hours(e.g., 3,000 hours). In one embodiment, for example, the ratio of thecapacitance after being exposed to the high temperature (e.g., 105° C.)for 3,000 hours to the initial capacitance value (e.g., at 23° C.) isfrom about 0.7 to 1, in some embodiments from about 0.8 to 1, in someembodiments from about 0.9 to 1, and in some embodiments, from 0.91 to0.99. The actual capacitance value (dry) may vary, but is typicallyabout 1 milliFarad per square centimeter (“mF/cm²”) or more, in someembodiments about 2 mF/cm² or more, in some embodiments from about 5 toabout 50 mF/cm², and in some embodiments, from about 8 to about 20mF/cm², measured at a frequency of 120 Hz.

In addition to those noted above, the capacitor may also exhibit otherimproved electrical properties. For instance, after being subjected toan applied voltage (e.g., 120 volts) for a period of time from about 30minutes to about 20 hours, in some embodiments from about 1 hour toabout 18 hours, and in some embodiments, from about 4 hours to about 16hours, the capacitor may exhibit a leakage current (“DCL”) of only about100 microamps (“μA”) or less, in some embodiments about 70 μA or less,and in some embodiments, from about 1 to about 50 μA. Notably, thecapacitor may exhibit such low DCL values even under dry conditions,such as described above. The capacitor may also exhibit a relatively lowequivalence series resistance (“ESR”), such as about 200 mohms, in someembodiments less than about 150 mohms, in some embodiments from about0.1 to about 125 mohms, and in some embodiments, from about 1 to about100 mohms, measured at an operating frequency of 100 kHz and temperatureof 23° C. The capacitor may also exhibit such ESR values even afterbeing exposed to a temperature of from about 80° C. or more, in someembodiments from about 100° C. to about 150° C., and in someembodiments, from about 105° C. to about 130° C. (e.g., 105° C. or 125°C.) for a substantial period of time, such as for about 100 hours ormore, and in some embodiments, from about 150 hours to about 3,000 hours(e.g., 3,000 hours). In one embodiment, for example, the ratio of theESR of the capacitor after being exposed to the high temperature (e.g.,105° C.) for 3,000 hours to the initial ESR value of the capacitor(e.g., at 23° C.) is about 2.0 or less, in some embodiments about 1.5 orless, and in some embodiments, from 1.0 to about 1.3.

It is also believed that the dissipation factor of the capacitor may bemaintained at relatively low levels. The dissipation factor generallyrefers to losses that occur in the capacitor and is usually expressed asa percentage of the ideal capacitor performance. For example, thedissipation factor of the capacitor is typically about 250% or less, insome embodiments about 200% or less, and in some embodiments, from about1% to about 180%, as determined at a frequency of 120 Hz.

Various embodiments of the capacitor will now be described in moredetail

I. Capacitor Element

A. Anode Body

The capacitor element includes an anode that contains a dielectricformed on an anode body. The anode body may be in the form of a sheet,foil, mesh, pellet, etc. Regardless of its form, the anode body istypically formed from a valve metal (i.e., metal that is capable ofoxidation) or valve metal-based compound, such as tantalum, niobium,aluminum, hafnium, titanium, alloys thereof, oxides thereof, nitridesthereof, and so forth. In one embodiment, for instance, the anode bodymay be in the form of a foil that contains aluminum. In anotherembodiment, the anode body may be in the form of a pellet that containstantalum, niobium, or an oxide thereof. A tantalum powder, for instance,may be formed from a reduction process in which a tantalum salt (e.g.,potassium fluorotantalate (K₂TaF₇), sodium fluorotantalate (Na₂TaF₇),tantalum pentachloride (TaCl₅), etc.) is reacted with a reducing agent.The reducing agent may be provided in the form of a liquid, gas (e.g.,hydrogen), or solid, such as a metal (e.g., sodium), metal alloy, ormetal salt. In one embodiment, for instance, a tantalum salt (e.g.,TaCl₅) may be heated at a temperature of from about 900° C. to about2,000° C., in some embodiments from about 1,000° C. to about 1,800° C.,and in some embodiments, from about 1,100° C. to about 1,600° C., toform a vapor that can be reduced in the presence of a gaseous reducingagent (e.g., hydrogen). Additional details of such a reduction reactionmay be described in WO 2014/199480 to Maeshima, et al. After thereduction, the product may be cooled, crushed, and washed to form apowder.

When employed, the specific charge of the powder typically varies fromabout 2,000 to about 600,000 microFarads*Volts per gram (“μF*V/g”)depending on the desired application. For instance, in certainembodiments, a high charge powder may be employed that has a specificcharge of from about 100,000 to about 600,000 μF*V/g, in someembodiments from about 120,000 to about 500,000 μF*V/g, and in someembodiments, from about 150,000 to about 400,000 μF*V/g. In otherembodiments, a low charge powder may be employed that has a specificcharge of from about 2,000 to about 100,000 μF*V/g, in some embodimentsfrom about 5,000 to about 80,000 μF*V/g, and in some embodiments, fromabout 10,000 to about 70,000 μF*V/g. As is known in the art, thespecific charge may be determined by multiplying capacitance by theanodizing voltage employed, and then dividing this product by the weightof the anodized electrode body. The powder may be a free-flowing, finelydivided powder that contains primary particles. The primary particles ofthe powder generally have a median size (D50) of from about 5 to about500 nanometers, in some embodiments from about 10 to about 400nanometers, and in some embodiments, from about 20 to about 250nanometers, such as determined using a laser particle size distributionanalyzer made by BECKMAN COULTER Corporation (e.g., LS-230), optionallyafter subjecting the particles to an ultrasonic wave vibration of 70seconds. The primary particles typically have a three-dimensionalgranular shape (e.g., nodular or angular). Such particles typically havea relatively low “aspect ratio”, which is the average diameter or widthof the particles divided by the average thickness (“D/T”). For example,the aspect ratio of the particles may be about 4 or less, in someembodiments about 3 or less, and in some embodiments, from about 1 toabout 2. In addition to primary particles, the powder may also containother types of particles, such as secondary particles formed byaggregating (or agglomerating) the primary particles. Such secondaryparticles may have a median size (D50) of from about 1 to about 500micrometers, and in some embodiments, from about 10 to about 250micrometers.

Agglomeration of the particles may occur by heating the particles and/orthrough the use of a binder. For example, agglomeration may occur at atemperature of from about 0° C. to about 40° C., in some embodimentsfrom about 5° C. to about 35° C., and in some embodiments, from about15° C. to about 30° C. Suitable binders may likewise include, forinstance, poly(vinyl butyral); poly(vinyl acetate); poly(vinyl alcohol);poly(vinyl pyrollidone); cellulosic polymers, such ascarboxymethylcellulose, methyl cellulose, ethyl cellulose, hydroxyethylcellulose, and methylhydroxyethyl cellulose; atactic polypropylene,polyethylene; polyethylene glycol (e.g., Carbowax from Dow ChemicalCo.); polystyrene, poly(butadiene/styrene); polyamides, polyimides, andpolyacrylamides, high molecular weight polyethers; copolymers ofethylene oxide and propylene oxide; fluoropolymers, such aspolytetrafluoroethylene, polyvinylidene fluoride, and fluoro-olefincopolymers; acrylic polymers, such as sodium polyacrylate, poly(loweralkyl acrylates), poly(lower alkyl methacrylates) and copolymers oflower alkyl acrylates and methacrylates; and fatty acids and waxes, suchas stearic and other soapy fatty acids, vegetable wax, microwaxes(purified paraffins), etc.

The resulting powder may be compacted to form a pellet using anyconventional powder press device. For example, a press mold may beemployed that is a single station compaction press containing a die andone or multiple punches. Alternatively, anvil-type compaction pressmolds may be used that use only a die and single lower punch. Singlestation compaction press molds are available in several basic types,such as cam, toggle/knuckle and eccentric/crank presses with varyingcapabilities, such as single action, double action, floating die,movable platen, opposed ram, screw, impact, hot pressing, coining orsizing. The powder may be compacted around an anode lead, which may bein the form of a wire, sheet, etc. The lead may extend in a longitudinaldirection from the anode body and may be formed from any electricallyconductive material, such as tantalum, niobium, aluminum, hafnium,titanium, etc., as well as electrically conductive oxides and/ornitrides of thereof. Connection of the lead to the anode body may alsobe accomplished using other known techniques, such as by welding thelead to the body or embedding it within the anode body during formation(e.g., prior to compaction and/or sintering).

Any binder may be removed after pressing by heating the pellet undervacuum at a certain temperature (e.g., from about 150° C. to about 500°C.) for several minutes. Alternatively, the binder may also be removedby contacting the pellet with an aqueous solution, such as described inU.S. Pat. No. 6,197,252 to Bishop, et al. Thereafter, the pellet issintered to form a porous, integral mass. The pellet is typicallysintered at a temperature of from about 700° C. to about 1800° C., insome embodiments from about 800° C. to about 1700° C., and in someembodiments, from about 900° C. to about 1400° C., for a time of fromabout 5 minutes to about 100 minutes, and in some embodiments, fromabout 8 minutes to about 15 minutes. This may occur in one or moresteps. If desired, sintering may occur in an atmosphere that limits thetransfer of oxygen atoms to the anode. For example, sintering may occurin a reducing atmosphere, such as in a vacuum, inert gas, hydrogen, etc.The reducing atmosphere may be at a pressure of from about 10 Torr toabout 2000 Torr, in some embodiments from about 100 Torr to about 1000Torr, and in some embodiments, from about 100 Torr to about 930 Torr.Mixtures of hydrogen and other gases (e.g., argon or nitrogen) may alsobe employed.

B. Dielectric

The anode is also coated with a dielectric. As indicated above, thedielectric is formed by anodically oxidizing (“anodizing”) the anode sothat a dielectric layer is formed over and/or within the anode. Forexample, a tantalum (Ta) anode may be anodized to tantalum pentoxide(Ta₂O₅), while an aluminum (Al) anode may be anodized to aluminumpentoxide (Al₂O₅).

Typically, anodization is performed by initially applying an electrolyteto the anode, such as by dipping anode into the electrolyte. Theelectrolyte is generally in the form of a liquid, such as a solution(e.g., aqueous or non-aqueous), dispersion, melt, etc. A solvent isgenerally employed in the electrolyte, such as water (e.g., deionizedwater); ethers (e.g., diethyl ether and tetrahydrofuran); glycols (e.g.,ethylene glycol, propylene glycol, etc.); alcohols (e.g., methanol,ethanol, n-propanol, isopropanol, and butanol); triglycerides; ketones(e.g., acetone, methyl ethyl ketone, and methyl isobutyl ketone); esters(e.g., ethyl acetate, butyl acetate, diethylene glycol ether acetate,and methoxypropyl acetate); amides (e.g., dimethylformamide,dimethylacetamide, dimethylcaprylic/capric fatty acid amide andN-alkylpyrrolidones); nitriles (e.g., acetonitrile, propionitrile,butyronitrile and benzonitrile); sulfoxides or sulfones (e.g., dimethylsulfoxide (DMSO) and sulfolane); and so forth. The solvent(s) mayconstitute from about 50 wt. % to about 99.9 wt. %, in some embodimentsfrom about 75 wt. % to about 99 wt. %, and in some embodiments, fromabout 80 wt. % to about 95 wt. % of the electrolyte. Although notnecessarily required, the use of an aqueous solvent (e.g., water) isoften desired to facilitate formation of an oxide. In fact, water mayconstitute about 1 wt. % or more, in some embodiments about 10 wt. % ormore, in some embodiments about 50 wt. % or more, in some embodimentsabout 70 wt. % or more, and in some embodiments, about 90 wt. % to 100wt. % of the solvent(s) used in the electrolyte.

The electrolyte is electrically conductive and may have an electricalconductivity of about 1 milliSiemens per centimeter (“mS/cm”) or more,in some embodiments about 30 mS/cm or more, and in some embodiments,from about 40 mS/cm to about 100 mS/cm, determined at a temperature of25° C. To enhance the electrical conductivity of the electrolyte, anionic compound is generally employed that is capable of dissociating inthe solvent to form ions. Suitable ionic compounds for this purpose mayinclude, for instance, acids, such as nitric acid, sulfuric acid,phosphoric acid, polyphosphoric acid, boric acid, boronic acid, etc.;organic acids, including carboxylic acids, such as acrylic acid,methacrylic acid, malonic acid, succinic acid, salicylic acid,sulfosalicylic acid, adipic acid, maleic acid, malic acid, oleic acid,gallic acid, tartaric acid, citric acid, formic acid, acetic acid,glycolic acid, oxalic acid, propionic acid, phthalic acid, isophthalicacid, glutaric acid, gluconic acid, lactic acid, aspartic acid,glutaminic acid, itaconic acid, trifluoroacetic acid, barbituric acid,cinnamic acid, benzoic acid, 4-hydroxybenzoic acid, aminobenzoic acid,etc.; sulfonic acids, such as methanesulfonic acid, benzenesulfonicacid, toluenesulfonic acid, trifluoromethanesulfonic acid,styrenesulfonic acid, naphthalene disulfonic acid,hydroxybenzenesulfonic acid, dodecylsulfonic acid,dodecylbenzenesulfonic acid, etc.; polymeric acids, such aspoly(acrylic) or poly(methacrylic) acid and copolymers thereof (e.g.,maleic-acrylic, sulfonic-acrylic, and styrene-acrylic copolymers),carageenic acid, carboxymethyl cellulose, alginic acid, etc.; and soforth. The concentration of ionic compounds is selected to achieve thedesired electrical conductivity. For example, an acid (e.g., phosphoricacid) may constitute from about 0.01 wt. % to about 5 wt. %, in someembodiments from about 0.05 wt. % to about 0.8 wt. %, and in someembodiments, from about 0.1 wt. % to about 0.5 wt. % of the electrolyte.If desired, blends of ionic compounds may also be employed in theelectrolyte.

To form the dielectric, a current is typically passed through theelectrolyte while it is in contact with the anode body. The value of theformation voltage manages the thickness of the dielectric layer. Forexample, the power supply may be initially set up at a galvanostaticmode until the required voltage is reached. Thereafter, the power supplymay be switched to a potentiostatic mode to ensure that the desireddielectric thickness is formed over the entire surface of the anode. Ofcourse, other known methods may also be employed, such as pulse or steppotentiostatic methods. The voltage at which anodic oxidation occurstypically ranges from about 4 to about 250 V, and in some embodiments,from about 5 to about 200 V, and in some embodiments, from about 10 toabout 150 V. During oxidation, the electrolyte can be kept at anelevated temperature, such as about 30° C. or more, in some embodimentsfrom about 40° C. to about 200° C., and in some embodiments, from about50° C. to about 100° C. Anodic oxidation can also be done at ambienttemperature or lower. The resulting dielectric layer may be formed on asurface of the anode and within its pores.

Although not required, in certain embodiments, the dielectric layer maypossess a differential thickness throughout the anode in that itpossesses a first portion that overlies an external surface of the anodeand a second portion that overlies an interior surface of the anode. Insuch embodiments, the first portion is selectively formed so that itsthickness is greater than that of the second portion. It should beunderstood, however, that the thickness of the dielectric layer need notbe uniform within a particular region. Certain portions of thedielectric layer adjacent to the external surface may, for example,actually be thinner than certain portions of the layer at the interiorsurface, and vice versa. Nevertheless, the dielectric layer may beformed such that at least a portion of the layer at the external surfacehas a greater thickness than at least a portion at the interior surface.Although the exact difference in these thicknesses may vary depending onthe particular application, the ratio of the thickness of the firstportion to the thickness of the second portion is typically from about1.2 to about 40, in some embodiments from about 1.5 to about 25, and insome embodiments, from about 2 to about 20.

To form a dielectric layer having a differential thickness, amulti-stage process may be employed. In each stage of the process, thesintered anode is anodically oxidized (“anodized”) to form a dielectriclayer (e.g., tantalum pentoxide). During the first stage of anodization,a relatively small forming voltage is typically employed to ensure thatthe desired dielectric thickness is achieved for the inner region, suchas forming voltages ranging from about 1 to about 90 volts, in someembodiments from about 2 to about 50 volts, and in some embodiments,from about 5 to about 20 volts. Thereafter, the sintered body may thenbe anodically oxidized in a second stage of the process to increase thethickness of the dielectric to the desired level. This is generallyaccomplished by anodizing in an electrolyte at a higher voltage thanemployed during the first stage, such as at forming voltages rangingfrom about 50 to about 350 volts, in some embodiments from about 60 toabout 300 volts, and in some embodiments, from about 70 to about 200volts. During the first and/or second stages, the electrolyte may bekept at a temperature within the range of from about 15° C. to about 95°C., in some embodiments from about 20° C. to about 90° C., and in someembodiments, from about 25° C. to about 85° C.

The electrolytes employed during the first and second stages of theanodization process may be the same or different. Typically, however,the electrolyte employed during at least one stage of the dielectricdevelopment process contains an ionic compound as explained above. Inone particular embodiment, it may be desired that the electrolyteemployed in the second stage has a lower ionic conductivity than theelectrolyte employed in the first stage to prevent a significant amountof oxide film from forming on the internal surface of anode. In thisregard, the electrolyte employed during the first stage may contain anionic compound that is an acid, such as nitric acid, sulfuric acid,phosphoric acid, polyphosphoric acid, boric acid, boronic acid, etc.Such an electrolyte may have an electrical conductivity of from about0.1 to about 100 mS/cm, in some embodiments from about 0.2 to about 20mS/cm, and in some embodiments, from about 1 to about 10 mS/cm,determined at a temperature of 25° C. The electrolyte employed duringthe second stage may likewise contain an ionic compound that is a saltof a weak acid so that the hydronium ion concentration increases in thepores as a result of charge passage therein. Ion transport or diffusionis such that the weak acid anion moves into the pores as necessary tobalance the electrical charges. As a result, the concentration of theprincipal conducting species (hydronium ion) is reduced in theestablishment of equilibrium between the hydronium ion, acid anion, andundissociated acid, thus forms a poorer-conducting species. Thereduction in the concentration of the conducting species results in arelatively high voltage drop in the electrolyte, which hinders furtheranodization in the interior while a thicker oxide layer, is being builtup on the outside to a higher formation voltage in the region ofcontinued high conductivity. Suitable weak acid salts may include, forinstance, ammonium or alkali metal salts (e.g., sodium, potassium, etc.)of boric acid, boronic acid, acetic acid, oxalic acid, lactic acid,adipic acid, etc. Particularly suitable salts include sodium tetraborateand ammonium pentaborate. Such electrolytes typically have an electricalconductivity of from about 0.1 to about 20 mS/cm, in some embodimentsfrom about 0.5 to about 10 mS/cm, and in some embodiments, from about 1to about 5 mS/cm, determined at a temperature of 25° C.

If desired, each stage of anodization may be repeated for one or morecycles to achieve the desired dielectric thickness. Furthermore, theanode may also be rinsed or washed with another solvent (e.g., water)after the first and/or second stages to remove the electrolyte.

C. Pre-Coat

A pre-coat is also employed that overlies the dielectric and positionedbetween the dielectric and the solid electrolyte. The pre-coat generallyincludes an organometallic compound, such as a compound having thefollowing general formula (II):

wherein,

Z is an organometallic atom, such as silicon, titanium, and so forth;

R₁, R₂, and R₃ are independently an alkyl (e.g., methyl, ethyl, propyl,etc.) or a hydroxyalkyl (e.g., hydroxymethyl, hydroxyethyl,hydroxypropyl, etc.), wherein at least one of R₁, R₂, and R₃ is ahydroxyalkyl;

n is an integer from 0 to 8, in some embodiments from 1 to 6, and insome embodiments, from 2 to 4 (e.g., 3); and

X is an organic or inorganic functional group, such as glycidyl,glycidyloxy, mercapto, amino, vinyl, etc.

In certain embodiments, at least one of R₁, R₂, and R₃ in Formula (II)may be a hydroxyalkyl (e.g., OCH₃). For example, each of R₁, R₂, and R₃may be a hydroxyalkyl. In other embodiments, however, R₁ may be an alkyl(e.g., CH₃) and R₂ and R₃ may a hydroxyalkyl (e.g., OCH₃).

In certain embodiments, X may be an amino group. Suitableaminofunctional organosilane compounds may include, for instance,monoamine functional silanes having the following general formula (II):

wherein,

R₁, R₂, and R₃ are as defined above;

R₄ and R₅ are independently hydrogen, alkyl, independently alkyl,alkenyl, aryl, heteroaryl, cycloalkyl, heterocyclyl, halo, haloalkyl,hydroxyalkyl, or alternatively N, R₄, and R₅ together with one or moreadditional atoms form a ring structure (e.g., heteroaryl orheterocyclyl); and

Z is an organic group that links the nitrogen atom to the silicon atom,such as alkyl (e.g., ethyl or propyl), aryl (e.g., phenyl), etc.

Examples of monoamino functional organosilane compounds may include, forinstance, primary amine compounds (e.g., 3-aminopropyltriethoxysilane,3-aminopropyltrimethoxysilane, 4-aminobutyltriethoxysilane,m-aminophenyltrimethoxysilane, p-aminophenyltrimethoxysilane,aminophenyltrimethoxysilane, 3-aminopropyltris(methoxy-ethoxy)silane,11-aminoundecyltriethoxysilane, 2(4-pyridylethyl)triethoxysilane,2-(trimethoxysilylethyl)pyridine, N-(3-trimethoxysilylpropyl)pyrrole,3-(m-aminophenoxypropyltrimethoxysilane, aminopropylsilanetriol,3-aminopropylmethyldiethoxysilane, 3-aminopropyldiisopropylethoxysilane,3-aminopropyldimethylethoxysilane, etc.); secondary amine compounds(e.g., N-butylaminopropyltrimethoxy silane,N-ethylaminoisobutyltrimethoxysilane,n-methylaminopropyltrimethoxysilane, N-phenylaminopropyltrimethoxysilane, 3-(N-allylamino)propyltrimethoxysilane,cyclohexylaminomethyl)triethoxysilane,N-cyclohexylaminopropyltrimethoxysilane,N-ethylaminoisobutylmethyldiethoxysilane,(phenylaminoethyl)methyl-diethoxysilane,N-phenylaminomethytrimethoxysilane,N-methylaminopropylmethyl-dimethoxysilane, etc.); tertiary aminecompounds (e.g., bis(2-hydroxyethyl)3-aminopropyltriethoxysilane,diethylaminomethyltriethoxysilane, (N,N-diethyl-3-aminopropyl)trimethoxysilane, etc.); as well as combinationsthereof. Further, if desired, an additional group may be bonded to thenitrogen atom so that the compound is a quaternary amine functionalsilane compound.

Diaminofunctional silane compounds may also be employed, such as thosehaving the following general formula (III):

wherein,

R₁, R₂, R₃, R₄, and R₅ are as defined above; and

Z₁ is an organic group that links the nitrogen atom to the silicon atomand Z₂ is an organic group that links the nitrogen atoms, such as alkyl(e.g., ethyl or propyl), aryl (e.g., phenyl), etc. Examples of suchdiaminofunctional silane compounds may include, for instance,N-(2-aminoethyl)-aminopropyltrimethoxysilane,N-(2-aminoethyl)-3-aminopropyltrimethoxysilane,N-(6-aminohexyl)aminomethyl-triethoxysilane,N-(6-aminohexyl)aminopropyltrimethoxysilane,N-(2-aminoethyl)-11-aminoundecyltrimethoxysilane),(aminoethylaminomethyl)-phenethyltrimethoxysilane,N-3-[(amino(polypropylenoxy)]-aminopropyltrimethoxysilane,N-(2-aminoethyl)-3-aminopropylsilanetriol,N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane,N-(2-aminoethyl)-3-aminoisobutylmethyldimethoxysilane,(aminoethylamino)-3-isobutyldimethylmethoxysilane, etc., as well ascombinations thereof. Triaminonfunctional compounds, such as(3-trimethoxysilylpropyl)-diethylenetrimamine, may also be employed.

Of course, as indicated above, other functional groups may also beemployed. For example, sulfur-functional silane compounds may beemployed in certain embodiments, such as3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane,2,2-dimethoxy-1-thia-2-silacyclopentane,11-mercaptoundecyltrimethoxysilane,S-(octanoyl)mercaptopropyltriethoxysilane,2-(2-pyridylethyl)thiopropyl-trimethoxysilane,2-(4-pyridethyl)thiopropyltrimethoxysilane,3-thiocyantopropyltrimethoxysilane,2-(3-trimethoxysilylpropylthio)-thiophene,mercaptomethylmethyldiethoxysilane,3-mercaptopropylmethyldimethoxysilane,bis[3-(triethoxysilyl)propyl]tetrasulfide,bis[3-(triethoxysilyl)propyl]disulfide,bis[m-(2-triethoxysilylethyl)tolyl]polysulfide,bis[3-(triethoxysilyl)propyl]thiourea, etc., as well as combinationsthereof. The particular manner in which the pre-coat is applied to thecapacitor body may vary as desired. In one particular embodiment, thecompound is dissolved in an organic solvent and applied to the part as asolution, such as by screen-printing, dipping, electrophoretic coating,spraying, etc. The organic solvent may vary, but is typically analcohol, such as methanol, ethanol, etc.

Organometallic compounds may constitute from about 0.1 wt. % to about 10wt. %, in some embodiments from about 0.2 wt. % to about 8 wt. %, and insome embodiments, from about 0.5 wt. % to about 5 wt. % of the solution.Solvents may likewise constitute from about 90 wt. % to about 99.9 wt.%, in some embodiments from about 92 wt. % to about 99.8 wt. %, and insome embodiments, from about 95 wt. % to about 99.5 wt. % of thesolution. Once applied, the part may then be dried to remove the solventtherefrom and form a pre-coat layer containing the organometalliccompound.

D. Solid Electrolyte

A solid electrolyte overlies the pre-coat and generally functions as thecathode for the capacitor. Typically, the total thickness of the solidelectrolyte is from about 1 to about 50 μm, and in some embodiments,from about 5 to about 20 μm. As indicated above, the solid electrolytecontains an intrinsically conductive polymer having repeating thiopheneunits of the following general formula (I):

wherein,

a is from 0 to 10, in some embodiments from 0 to 6, and in someembodiments, from 1 to 4 (e.g., 1);

b is from 1 to 18, in some embodiments from 1 to 10, and in someembodiments, from 2 to 6 (e.g., 2, 3, 4, or 5);

R is an optionally substituted C₁-C₆ linear or branched alkyl group(e.g., methyl) or a halogen atom (e.g., fluorine);

M is a hydrogen atom, an alkali metal (e.g., Li, Na, or K), NH(R¹)₃, orHNC₅H₅, wherein R¹ is each independently a hydrogen atom or anoptionally substituted C₁-C₆ alkyl group.

Specific examples of thiophene compounds used to form such repeating aredescribed in U.S. Pat. No. 9,718,905 and may include, for instance,sodium3-[(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate,sodium3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-ethyl-1-propanesulfonate,sodium3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-propyl-1-propane-sulfonate,sodium3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-butyl-1-propanesulfonate,sodium3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-pentyl-1-propane-sulfonate,sodium3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-hexyl-1-propanesulfonate,sodium3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-isopropyl-1-propanesulfonate,sodium3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-isobutyl-1-propanesulfonate,sodium3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-isopentyl-1-propanesulfonate,sodium3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-fluoro-1-propanesulfonate,potassium3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate,3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonicacid, ammonium3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propane-sulfonate,triethylammonium3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate,etc., as well as combination thereof. Each of the above exemplifiedthiophene monomers may be prepared fromthieno[3,4-b]-1,4-dioxin-2-methanol and a branched sultone compound inaccordance with a known method (e.g., Journal of ElectroanalyticalChemistry, 443, 217 to 226 (1998)).

The intrinsically conductive polymer may be formed through a variety oftechniques as would be understood by those skilled in the art. In oneparticular embodiment, for example, a thiophene compound having thegeneral formula (I) may be polymerized in the presence of an oxidativecatalyst. Derivatives of these monomers may also be employed that are,for example, dimers or trimers of the above compounds. The derivativesmay be made up of identical or different monomer units and used in pureform and in a mixture with one another and/or with the monomers.Oxidized or reduced forms of these precursors may also be employed. Theamount of the oxidizing catalyst used in this polymerization reaction isnot particularly limited, and may be within a range of from 1 to 50molar times, more preferably from 1 to 20 molar times to the number ofmoles of the thiophene compound used as a material charged. Theoxidative catalyst may be a transition metal salt, such as a salt of aninorganic or organic acid that contain ammonium, sodium, gold, iron(II),copper(II), chromium(VI), cerium(IV), manganese(IV), manganese(VII), orruthenium(III) cations. Particularly suitable transition metal saltsinclude halides (e.g., FeCl₃ or HAuCl₄); salts of other inorganic acids(e.g., Fe(ClO₄)₃, Fe₂(SO₄)₃, (NH₄)₂S₂O₈, or Na₃Mo₁₂PO₄₀); and salts oforganic acids and inorganic acids comprising organic radicals. Examplesof salts of inorganic acids with organic radicals include, for instance,iron(III) salts of sulfuric acid monoesters of C₁ to C₂₀ alkanols (e.g.,iron(III) salt of lauryl sulfate). Likewise, examples of salts oforganic acids include, for instance, iron(III) salts of C₁ to C₂₀ alkanesulfonic acids (e.g., methane, ethane, propane, butane, or dodecanesulfonic acid); iron (III) salts of aliphatic perfluorosulfonic acids(e.g., trifluoromethane sulfonic acid, perfluorobutane sulfonic acid, orperfluorooctane sulfonic acid); iron (III) salts of aliphatic C₁ to C₂₀carboxylic acids (e.g., 2-ethylhexylcarboxylic acid); iron (III) saltsof aliphatic perfluorocarboxylic acids (e.g., trifluoroacetic acid orperfluorooctane acid); iron (III) salts of aromatic sulfonic acidsoptionally substituted by C₁ to C₂₀ alkyl groups (e.g., benzene sulfonicacid, o-toluene sulfonic acid, p-toluene sulfonic acid, ordodecylbenzene sulfonic acid); iron (III) salts of cycloalkane sulfonicacids (e.g., camphor sulfonic acid); and so forth. Mixtures of theseabove-mentioned salts may also be used.

Oxidative polymerization generally occurs in the presence of one or moresolvents. Suitable solvents may include, for instance, water, glycols(e.g., ethylene glycol, propylene glycol, butylene glycol, triethyleneglycol, hexylene glycol, polyethylene glycols, ethoxydiglycol,dipropyleneglycol, etc.); glycol ethers (e.g., methyl glycol ether,ethyl glycol ether, isopropyl glycol ether, etc.); alcohols (e.g.,methanol, ethanol, n-propanol, iso-propanol, and butanol); ketones(e.g., acetone, methyl ethyl ketone, and methyl isobutyl ketone); esters(e.g., ethyl acetate, butyl acetate, diethylene glycol ether acetate,methoxypropyl acetate, ethylene carbonate, propylene carbonate, etc.);amides (e.g., dimethylformamide, dimethylacetamide,dimethylcaprylic/capric fatty acid amide and N-alkylpyrrolidones);sulfoxides or sulfones (e.g., dimethyl sulfoxide (DMSO) and sulfolane);phenolic compounds (e.g., toluene, xylene, etc.), and so forth. Water isa particularly suitable solvent for the reaction. The amount of thesolvent used in this polymerization reaction is not particularly limitedso long as the thiophene compound used as a material is dissolved in thesolvent, however, it is preferably from 0.1 to 100 times, morepreferably from 0.1 to 50 times the weight of the thiophene compoundcharged. The temperature at which the reaction occurs typically variesfrom about −20° C. to about 140° C., and in some embodiments, from about20° C. to about 100° C. Upon completion of the reaction, knownpurification techniques may be employed to remove any salt impurities,such by washing with a solvent, re-precipitation, centrifugalsedimentation, ultrafiltration, dialysis or ion exchange resintreatment, etc., as well as combination thereof.

Regardless of how it is formed, the polymer is considered“intrinsically” conductive to the extent that it has a positive chargelocated on the main chain that is at least partially compensated byanions covalently bound to the polymer. The polymer may, for example,have a relatively high specific conductivity, in the dry state, of about1 Siemen per centimeter (“S/cm”) or more, in some embodiments about 10S/cm or more, in some embodiments about 25 S/cm or more, in someembodiments about 40 S/cm or more, and in some embodiments, from about50 to about 500 S/cm. As a result of its intrinsic conductivity, thesolid electrolyte does not require the addition of conventional dopants,such as polystyrene sulfonic acid. In fact, the solid electrolyte may besubstantially free of such dopants. Nevertheless, it should beunderstood that dopants may be employed in certain embodiments of thepresent invention. When utilized, however, dopants are typically presentin the solid electrolyte in an amount of about 5 wt. % or less, in someembodiments about 2 wt. % or less, and in some embodiments, about 1 wt.% or less.

The polymer is also generally highly soluble in water, which enables itto be more easily and effectively applied to the anode. The solublepolymer is also able to more readily impregnate the small pores formedby the high specific charge powder, so that the resulting solidelectrolyte has a “film-like” configuration and coats at least a portionof the anode in a substantially uniform manner. This improves thequality of the resulting oxide as well as its surface coverage, andthereby enhances the electrical properties of the capacitor assembly.

i. Inner Layers

The solid electrolyte is generally formed from one or more “inner”conductive polymer layers. The term “inner” in this context refers toone or more layers formed from the same material and that overly thepre-coat, whether directly or via another layer. The inner layer(s), forexample, typically contain an intrinsically conductive polymer such asdescribed above. In one particular embodiment, the inner layer(s) aregenerally free of extrinsically conductive polymers and thus formedprimarily from intrinsically conductive polymers. More particularly,intrinsically conductive polymers may constitute about 50 wt. % or more,in some embodiments about 70 wt. % or more, and in some embodiments,about 90 wt. % or more (e.g., 100 wt. %) of the inner layer(s). One ormultiple inner layers may be employed. For example, the solidelectrolyte typically contains from 2 to 30, in some embodiments from 4to 20, and in some embodiments, from about 5 to 15 inner layers (e.g.,10 layers).

The inner layer(s) may be applied in the form of a solution containing asolvent. The concentration of the polymer may vary depending on thedesired viscosity of and the particular manner in which the layer is tobe applied to the anode. Typically, however, the polymer constitutesfrom about 0.1 to about 10 wt. %, in some embodiments from about 0.4 toabout 5 wt. %, and in some embodiments, from about 0.5 to about 4 wt. %of the solution. Solvent(s) may likewise constitute from about 90 wt. %to about 99.9 wt. %, in some embodiments from about 95 wt. % to about99.6 wt. %, and in some embodiments, from about 96 wt. % to about 99.5wt. % of the solution. While other solvents may certainly be employed,it is generally desired that water is the primary solvent such that thesolution is considered an “aqueous” solution. In most embodiments, forexample, water constitutes at least about 50 wt. %, in some embodimentsat least about 75 wt. %, and in some embodiments, from about 90 wt. % to100 wt. % of the solvent(s) employed. When employed, a solution may beapplied to the anode using any known technique, such as dipping, casting(e.g., curtain coating, spin coating, etc.), printing (e.g., gravureprinting, offset printing, screen printing, etc.), and so forth. Theresulting conductive polymer layer may be dried and/or washed after itis applied to the anode.

ii. Outer Layers

The solid electrolyte may contain only “inner layers” so that it isessentially formed from the same material, i.e., intrinsicallyconductive polymers. Nevertheless, in other embodiments, the solidelectrolyte may also contain one or more optional “outer” conductivepolymer layers that are formed from a different material than the innerlayer(s) and overly the inner layer(s). For example, the outer layer(s)may be formed from an extrinsically conductive polymer. In oneparticular embodiment, the outer layer(s) are formed primarily from suchextrinsically conductive polymers in that they constitute about 50 wt. %or more, in some embodiments about 70 wt. % or more, and in someembodiments, about 90 wt. % or more (e.g., 100 wt. %) of a respectiveouter layer. One or multiple outer layers may be employed. For example,the solid electrolyte may contain from 2 to 30, in some embodiments from4 to 20, and in some embodiments, from about 5 to 15 outer layers.

When employed, the extrinsically conductive polymer may, for instance,have repeating units of the following formula (IV):

wherein,

R₇ is a linear or branched, C₁ to C₁₈ alkyl radical (e.g., methyl,ethyl, n- or iso-propyl, n-, iso-, sec- or tert-butyl, n-pentyl,1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1-ethylpropyl,1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, n-hexyl,n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl,n-tridecyl, n-tetradecyl, n-hexadecyl, n-octadecyl, etc.); C₅ to C₁₂cycloalkyl radical (e.g., cyclopentyl, cyclohexyl, cycloheptyl,cyclooctyl, cyclononyl, cyclodecyl, etc.); C₁ to C₁₄ aryl radical (e.g.,phenyl, naphthyl, etc.); C₇ to C₁₈ aralkyl radical (e.g., benzyl, o-,m-, p-tolyl, 2,3-, 2,4-, 2,5-, 2-6, 3-4-, 3,5-xylyl, mesityl, etc.); C₁to C₄ hydroxyalkyl radical, or hydroxyl radical; and

q is an integer from 0 to 8, in some embodiments, from 0 to 2, and inone embodiment, 0. In one particular embodiment, “q” is 0 and thepolymer is poly(3,4-ethylenedioxythiophene). One commercially suitableexample of a monomer suitable for forming such a polymer is3,4-ethylenedioxthiophene, which is available from Heraeus under thedesignation Clevios™ M.

The polymers of formula (IV) are generally considered to be“extrinsically” conductive to the extent that they require the presenceof a separate counterion that is not covalently bound to the polymer.The counterion may be a monomeric or polymeric anion that counteractsthe charge of the conductive polymer. Polymeric anions can, for example,be anions of polymeric carboxylic acids (e.g., polyacrylic acids,polymethacrylic acid, polymaleic acids, etc.); polymeric sulfonic acids(e.g., polystyrene sulfonic acids (“PSS”), polyvinyl sulfonic acids,etc.); and so forth. The acids may also be copolymers, such ascopolymers of vinyl carboxylic and vinyl sulfonic acids with otherpolymerizable monomers, such as acrylic acid esters and styrene.Likewise, suitable monomeric anions include, for example, anions of C₁to C₂₀ alkane sulfonic acids (e.g., dodecane sulfonic acid); aliphaticperfluorosulfonic acids (e.g., trifluoromethane sulfonic acid,perfluorobutane sulfonic acid or perfluorooctane sulfonic acid);aliphatic C₁ to C₂₀ carboxylic acids (e.g., 2-ethyl-hexylcarboxylicacid); aliphatic perfluorocarboxylic acids (e.g., trifluoroacetic acidor perfluorooctanoic acid); aromatic sulfonic acids optionallysubstituted by C₁ to C₂₀ alkyl groups (e.g., benzene sulfonic acid,o-toluene sulfonic acid, p-toluene sulfonic acid or dodecylbenzenesulfonic acid); cycloalkane sulfonic acids (e.g., camphor sulfonic acidor tetrafluoroborates, hexafluorophosphates, perchlorates,hexafluoroantimonates, hexafluoroarsenates or hexachloroantimonates);and so forth. Particularly suitable counteranions are polymeric anions,such as a polymeric carboxylic or sulfonic acid (e.g., polystyrenesulfonic acid (“PSS”)). The molecular weight of such polymeric anionstypically ranges from about 1,000 to about 2,000,000, and in someembodiments, from about 2,000 to about 500,000.

When employed, it may be desirable that the extrinsically conductivepolymer is applied in the form of a dispersion of pre-polymerizedconductive particles. Such particles typically have an average size(e.g., diameter) of from about 1 to about 100 nanometers, in someembodiments from about 2 to about 80 nanometers, and in someembodiments, from about 4 to about 50 nanometers. The diameter of theparticles may be determined using known techniques, such as byultracentrifuge, laser diffraction, etc. The shape of the particles maylikewise vary. In one particular embodiment, for instance, the particlesare spherical in shape. However, it should be understood that othershapes are also contemplated by the present invention, such as plates,rods, discs, bars, tubes, irregular shapes, etc. The concentration ofthe particles in the dispersion may vary depending on the desiredviscosity of the dispersion and the particular manner in which thedispersion is to be applied to the capacitor element. Typically,however, the particles constitute from about 0.1 to about 10 wt. %, insome embodiments from about 0.4 to about 5 wt. %, and in someembodiments, from about 0.5 to about 4 wt. % of the dispersion.

The dispersion may also contain one or more binders to further enhancethe adhesive nature of the polymeric layer and also increase thestability of the particles within the dispersion. The binders may beorganic in nature, such as polyvinyl alcohols, polyvinyl pyrrolidones,polyvinyl chlorides, polyvinyl acetates, polyvinyl butyrates,polyacrylic acid esters, polyacrylic acid amides, polymethacrylic acidesters, polymethacrylic acid amides, polyacrylonitriles, styrene/acrylicacid ester, vinyl acetate/acrylic acid ester and ethylene/vinyl acetatecopolymers, polybutadienes, polyisoprenes, polystyrenes, polyethers,polyesters, polycarbonates, polyurethanes, polyamides, polyimides,polysulfones, melamine formaldehyde resins, epoxide resins, siliconeresins or celluloses. Crosslinking agents may also be employed toenhance the adhesion capacity of the binders. Such crosslinking agentsmay include, for instance, melamine compounds, masked isocyanates orfunctional silanes, such as 3-glycidoxypropyltrialkoxysilane,tetraethoxysilane and tetraethoxysilane hydrolysate or crosslinkablepolymers, such as polyurethanes, polyacrylates or polyolefins, andsubsequent crosslinking.

Dispersion agents may also be employed to facilitate the ability toapply the layer to the anode. Suitable dispersion agents includesolvents, such as aliphatic alcohols (e.g., methanol, ethanol,i-propanol and butanol), aliphatic ketones (e.g., acetone and methylethyl ketones), aliphatic carboxylic acid esters (e.g., ethyl acetateand butyl acetate), aromatic hydrocarbons (e.g., toluene and xylene),aliphatic hydrocarbons (e.g., hexane, heptane and cyclohexane),chlorinated hydrocarbons (e.g., dichloromethane and dichloroethane),aliphatic nitriles (e.g., acetonitrile), aliphatic sulfoxides andsulfones (e.g., dimethyl sulfoxide and sulfolane), aliphatic carboxylicacid amides (e.g., methylacetamide, dimethylacetamide anddimethylformamide), aliphatic and araliphatic ethers (e.g., diethyletherand anisole), water, and mixtures of any of the foregoing solvents. Aparticularly suitable dispersion agent is water.

In addition to those mentioned above, still other ingredients may alsobe used in the dispersion. For example, conventional fillers may be usedthat have a size of from about 10 nanometers to about 100 micrometers,in some embodiments from about 50 nanometers to about 50 micrometers,and in some embodiments, from about 100 nanometers to about 30micrometers. Examples of such fillers include calcium carbonate,silicates, silica, calcium or barium sulfate, aluminum hydroxide, glassfibers or bulbs, wood flour, cellulose powder carbon black, electricallyconductive polymers, etc. The fillers may be introduced into thedispersion in powder form, but may also be present in another form, suchas fibers.

Surface-active substances may also be employed in the dispersion, suchas ionic or non-ionic surfactants. Furthermore, adhesives may beemployed, such as organofunctional silanes or their hydrolysates, forexample 3-glycidoxypropyltrialkoxysilane, 3-aminopropyl-triethoxysilane,3-mercaptopropyltrimethoxysilane, 3-metacryloxypropyltrimethoxysilane,vinyltrimethoxysilane or octyltriethoxysilane. The dispersion may alsocontain additives that increase conductivity, such as ethergroup-containing compounds (e.g., tetrahydrofuran), lactonegroup-containing compounds (e.g., γ-butyrolactone or γ-valerolactone),amide or lactam group-containing compounds (e.g., caprolactam,N-methylcaprolactam, N,N-dimethylacetamide, N-methylacetamide,N,N-dimethylformamide (DMF), N-methylformamide, N-methylformanilide,N-methylpyrrolidone (NMP), N-octylpyrrolidone, or pyrrolidone), sulfonesand sulfoxides (e.g., sulfolane (tetramethylenesulfone) ordimethylsulfoxide (DMSO)), sugar or sugar derivatives (e.g., saccharose,glucose, fructose, or lactose), sugar alcohols (e.g., sorbitol ormannitol), furan derivatives (e.g., 2-furancarboxylic acid or3-furancarboxylic acid), an alcohols (e.g., ethylene glycol, glycerol,di- or triethylene glycol).

The dispersion may be applied using a variety of known techniques, suchas by spin coating, impregnation, pouring, dropwise application,injection, spraying, doctor blading, brushing, printing (e.g., ink-jet,screen, or pad printing), or dipping. The viscosity of the dispersion istypically from about 0.1 to about 100,000 mPas (measured at a shear rateof 100 s⁻¹), in some embodiments from about 1 to about 10,000 mPas, insome embodiments from about 10 to about 1,500 mPas, and in someembodiments, from about 100 to about 1000 mPas.

If desired, a hydroxyl-functional nonionic polymer may also be employedin the outer layer(s) of the solid electrolyte. The term“hydroxy-functional” generally means that the compound contains at leastone hydroxyl functional group or is capable of possessing such afunctional group in the presence of a solvent. Without intending to belimited by theory, it is believed that the use of a hydroxy-functionalpolymer with a certain molecular weight can minimize the likelihood ofchemical decomposition at high voltages. For instance, the molecularweight of the hydroxy-functional polymer may be from about 100 to 10,000grams per mole, in some embodiments from about 200 to 2,000, in someembodiments from about 300 to about 1,200, and in some embodiments, fromabout 400 to about 800.

Any of a variety of hydroxy-functional nonionic polymers may generallybe employed for this purpose. In one embodiment, for example, thehydroxy-functional polymer is a polyalkylene ether. Polyalkylene ethersmay include polyalkylene glycols (e.g., polyethylene glycols,polypropylene glycols polytetramethylene glycols, polyepichlorohydrins,etc.), polyoxetanes, polyphenylene ethers, polyether ketones, and soforth. Polyalkylene ethers are typically predominantly linear, nonionicpolymers with terminal hydroxy groups. Particularly suitable arepolyethylene glycols, polypropylene glycols and polytetramethyleneglycols (polytetrahydrofurans), which are produced by polyaddition ofethylene oxide, propylene oxide or tetrahydrofuran onto water. Thepolyalkylene ethers may be prepared by polycondensation reactions fromdiols or polyols. The diol component may be selected, in particular,from saturated or unsaturated, branched or unbranched, aliphaticdihydroxy compounds containing 5 to 36 carbon atoms or aromaticdihydroxy compounds, such as, for example, pentane-1,5-diol,hexane-1,6-diol, neopentyl glycol, bis-(hydroxymethyl)-cyclohexanes,bisphenol A, dimer diols, hydrogenated dimer diols or even mixtures ofthe diols mentioned. In addition, polyhydric alcohols may also be usedin the polymerization reaction, including for example glycerol, di- andpolyglycerol, trimethylolpropane, pentaerythritol or sorbitol.

In addition to those noted above, other hydroxy-functional nonionicpolymers may also be employed in the present invention. Some examples ofsuch polymers include, for instance, ethoxylated alkylphenols;ethoxylated or propoxylated C₆-C₂₄ fatty alcohols; polyoxyethyleneglycol alkyl ethers having the general formula:CH₃—(CH₂)₁₀₋₁₆—(O—C₂H₄)₁₋₂₅—OH (e.g., octaethylene glycol monododecylether and pentaethylene glycol monododecyl ether); polyoxypropyleneglycol alkyl ethers having the general formula:CH₃—(CH₂)₁₀₋₁₆—(O—C₃H₆)₁₋₂₅—OH; polyoxyethylene glycol octylphenolethers having the following general formula:C₈H₁₇—(C₆H₄)—(O—C₂H₄)₁₋₂₅—OH (e.g., Triton™ X-100); polyoxyethyleneglycol alkylphenol ethers having the following general formula:CH₉—(C₆H₄)—(O—C₂H₄)₁₋₂₅—OH (e.g., nonoxynol-9); polyoxyethylene glycolesters of C₈-C₂₄ fatty acids, such as polyoxyethylene glycol sorbitanalkyl esters (e.g., polyoxyethylene (20) sorbitan monolaurate,polyoxyethylene (20) sorbitan monopalmitate, polyoxyethylene (20)sorbitan monostearate, polyoxyethylene (20) sorbitan monooleate, PEG-20methyl glucose distearate, PEG-20 methyl glucose sesquistearate, PEG-80castor oil, and PEG-20 castor oil, PEG-3 castor oil, PEG 600 dioleate,and PEG 400 dioleate) and polyoxyethylene glycerol alkyl esters (e.g.,polyoxyethylene-23 glycerol laurate and polyoxyethylene-20 glycerolstearate); polyoxyethylene glycol ethers of C₈-C₂₄ fatty acids (e.g.,polyoxyethylene-10 cetyl ether, polyoxyethylene-10 stearyl ether,polyoxyethylene-20 cetyl ether, polyoxyethylene-10 oleyl ether,polyoxyethylene-20 oleyl ether, polyoxyethylene-20 isohexadecyl ether,polyoxyethylene-15 tridecyl ether, and polyoxyethylene-6 tridecylether); block copolymers of polyethylene glycol and polypropylene glycol(e.g., Poloxamers); and so forth, as well as mixtures thereof.

The hydroxy-functional nonionic polymer may be incorporated into theouter layers in a variety of different ways. In certain embodiments, forinstance, the nonionic polymer may simply be incorporated into thedispersion of extrinsically conductive polymers. In such embodiments,the concentration of the nonionic polymer in the layer may be from about1 wt. % to about 50 wt. %, in some embodiments from about 5 wt. % toabout 40 wt. %, and in some embodiments, from about 10 wt. % to about 30wt. %. In other embodiments, however, the nonionic polymer may beapplied after the initial outer layer(s) are formed. In suchembodiments, the technique used to apply the nonionic polymer may vary.For example, the nonionic polymer may be applied in the form of a liquidsolution using various methods, such as immersion, dipping, pouring,dripping, injection, spraying, spreading, painting or printing, forexample, inkjet, screen printing or tampon printing. Solvents known tothe person skilled in the art can be employed in the solution, such aswater, alcohols, or a mixture thereof. The concentration of the nonionicpolymer in such a solution typically ranges from about 5 wt. % to about95 wt. %, in some embodiments from about 10 wt. % to about 70 wt. %, andin some embodiments, from about 15 wt. % to about 50 wt. % of thesolution. If desired, such solutions may be generally free of conductivepolymers. For example, conductive polymers may constitute about 2 wt. %or less, in some embodiments about 1 wt. % or less, and in someembodiments, about 0.5 wt. % or less of the solution.

E. External Polymer Coating

If desired, an external polymer coating may also be applied to the anodethat overlies the solid electrolyte. When employed, the external polymercoating generally contains one or more layers formed from conductivepolymer particles, such as described above (e.g., formed from anextrinsically conductive polymer). The external coating may be able tofurther penetrate into the edge region of the capacitor body to increasethe adhesion to the dielectric and result in a more mechanically robustpart, which may reduce equivalent series resistance and leakage current.Because it is generally intended to improve the degree of edge coveragerather to impregnate the interior of the anode body, the particles usedin the external coating typically have a larger size than those employedin any optional particles employed in the solid electrolyte (e.g., inthe outer layer(s)). For example, the ratio of the average size of theparticles employed in the external polymer coating to the average sizeof any particles employed in the solid electrolyte is typically fromabout 1.5 to about 30, in some embodiments from about 2 to about 20, andin some embodiments, from about 5 to about 15. For example, theparticles employed in the external coating may have an average size offrom about 50 to about 800 nanometers, in some embodiments from about 80to about 600 nanometers, and in some embodiments, from about 100 toabout 500 nanometers.

A crosslinking agent may also be optionally employed in the externalpolymer coating to further enhance the degree of adhesion to the solidelectrolyte. Typically, the crosslinking agent is applied prior toapplication of the dispersion used in the external coating. Suitablecrosslinking agents are described, for instance, in U.S. PatentPublication No. 2007/0064376 to Merker, et al. and include, forinstance, amines (e.g., diamines, triamines, oligomer amines,polyamines, etc.); polyvalent metal cations, such as salts or compoundsof Mg, Al, Ca, Fe, Cr, Mn, Ba, Ti, Co, Ni, Cu, Ru, Ce or Zn, phosphoniumcompounds, sulfonium compounds, etc. Particularly suitable examplesinclude, for instance, 1,4-diaminocyclohexane,1,4-bis(amino-methyl)cyclohexane, ethylenediamine, 1,6-hexanediamine,1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine,1,10-decanediamine, 1,12-dodecanediamine, N,N-dimethylethylenediamine,N,N,N′,N′-tetramethylethylenediamine,N,N,N′,N′-tetramethyl-1,4-butanediamine, etc., as well as mixturesthereof.

The crosslinking agent is typically applied from a solution ordispersion whose pH is from 1 to 10, in some embodiments from 2 to 7, insome embodiments, from 3 to 6, as determined at 25° C. Acidic compoundsmay be employed to help achieve the desired pH level. Examples ofsolvents or dispersants for the crosslinking agent include water ororganic solvents, such as alcohols, ketones, carboxylic esters, etc. Thecrosslinking agent may be applied to the capacitor body by any knownprocess, such as spin-coating, impregnation, casting, dropwiseapplication, spray application, vapor deposition, sputtering,sublimation, knife-coating, painting or printing, for example inkjet,screen or pad printing. Once applied, the crosslinking agent may bedried prior to application of the polymer dispersion. This process maythen be repeated until the desired thickness is achieved. For example,the total thickness of the entire external polymer coating, includingthe crosslinking agent and dispersion layers, may range from about 1 toabout 50 μm, in some embodiments from about 2 to about 40 μm, and insome embodiments, from about 5 to about 20 μm.

F. Cathode Coating

If desired, the capacitor element may also employ a cathode coating thatoverlies the solid electrolyte and external polymer coating. The cathodecoating may contain a metal particle layer includes a plurality ofconductive metal particles dispersed within a polymer matrix. Theparticles typically constitute from about 50 wt. % to about 99 wt. %, insome embodiments from about 60 wt. % to about 98 wt. %, and in someembodiments, from about 70 wt. % to about 95 wt. % of the layer, whilethe polymer matrix typically constitutes from about 1 wt. % to about 50wt. %, in some embodiments from about 2 wt. % to about 40 wt. %, and insome embodiments, from about 5 wt. % to about 30 wt. % of the layer.

The conductive metal particles may be formed from a variety of differentmetals, such as copper, nickel, silver, nickel, zinc, tin, lead, copper,aluminum, molybdenum, titanium, iron, zirconium, magnesium, etc., aswell as alloys thereof. Silver is a particularly suitable conductivemetal for use in the layer. The metal particles often have a relativelysmall size, such as an average size of from about 0.01 to about 50micrometers, in some embodiments from about 0.1 to about 40 micrometers,and in some embodiments, from about 1 to about 30 micrometers.Typically, only one metal particle layer is employed, although it shouldbe understood that multiple layers may be employed if so desired. Thetotal thickness of such layer(s) is typically within the range of fromabout 1 μm to about 500 μm, in some embodiments from about 5 μm to about200 μm, and in some embodiments, from about 10 μm to about 100 μm.

The polymer matrix typically includes a polymer, which may bethermoplastic or thermosetting in nature. Typically, however, thepolymer is selected so that it can act as a barrier to electromigrationof silver ions, and also so that it contains a relatively small amountof polar groups to minimize the degree of water adsorption in thecathode coating. In this regard, the present inventors have found thatvinyl acetal polymers are particularly suitable for this purpose, suchas polyvinyl butyral, polyvinyl formal, etc. Polyvinyl butyral, forinstance, may be formed by reacting polyvinyl alcohol with an aldehyde(e.g., butyraldehyde). Because this reaction is not typically complete,polyvinyl butyral will generally have a residual hydroxyl content. Byminimizing this content, however, the polymer can possess a lesserdegree of strong polar groups, which would otherwise result in a highdegree of moisture adsorption and result in silver ion migration. Forinstance, the residual hydroxyl content in polyvinyl acetal may be about35 mol. % or less, in some embodiments about 30 mol. % or less, and insome embodiments, from about 10 mol. % to about 25 mol. %. Onecommercially available example of such a polymer is available fromSekisui Chemical Co., Ltd. under the designation “BH—S” (polyvinylbutyral).

To form the cathode coating, a conductive paste is typically applied tothe capacitor that overlies the solid electrolyte. One or more organicsolvents are generally employed in the paste. A variety of differentorganic solvents may generally be employed, such as glycols (e.g.,propylene glycol, butylene glycol, triethylene glycol, hexylene glycol,polyethylene glycols, ethoxydiglycol, and dipropyleneglycol); glycolethers (e.g., methyl glycol ether, ethyl glycol ether, and isopropylglycol ether); ethers (e.g., diethyl ether and tetrahydrofuran);alcohols (e.g., benzyl alcohol, methanol, ethanol, n-propanol,iso-propanol, and butanol); triglycerides; ketones (e.g., acetone,methyl ethyl ketone, and methyl isobutyl ketone); esters (e.g., ethylacetate, butyl acetate, diethylene glycol ether acetate, andmethoxypropyl acetate); amides (e.g., dimethylformamide,dimethylacetamide, dimethylcaprylic/capric fatty acid amide andN-alkylpyrrolidones); nitriles (e.g., acetonitrile, propionitrile,butyronitrile and benzonitrile); sulfoxides or sulfones (e.g., dimethylsulfoxide (DMSO) and sulfolane); etc., as well as mixtures thereof. Theorganic solvent(s) typically constitute from about 10 wt. % to about 70wt. %, in some embodiments from about 20 wt. % to about 65 wt. %, and insome embodiments, from about 30 wt. % to about 60 wt. %. of the paste.Typically, the metal particles constitute from about 10 wt. % to about60 wt. %, in some embodiments from about 20 wt. % to about 45 wt. %, andin some embodiments, from about 25 wt. % to about 40 wt. % of the paste,and the resinous matrix constitutes from about 0.1 wt. % to about 20 wt.%, in some embodiments from about 0.2 wt. % to about 10 wt. %, and insome embodiments, from about 0.5 wt. % to about 8 wt. % of the paste.

The paste may have a relatively low viscosity, allowing it to be readilyhandled and applied to a capacitor element. The viscosity may, forinstance, range from about 50 to about 3,000 centipoise, in someembodiments from about 100 to about 2,000 centipoise, and in someembodiments, from about 200 to about 1,000 centipoise, such as measuredwith a Brookfield DV-1 viscometer (cone and plate) operating at a speedof 10 rpm and a temperature of 25° C. If desired, thickeners or otherviscosity modifiers may be employed in the paste to increase or decreaseviscosity. Further, the thickness of the applied paste may also berelatively thin and still achieve the desired properties. For example,the thickness of the paste may be from about 0.01 to about 50micrometers, in some embodiments from about 0.5 to about 30 micrometers,and in some embodiments, from about 1 to about 25 micrometers. Onceapplied, the metal paste may be optionally dried to remove certaincomponents, such as the organic solvents. For instance, drying may occurat a temperature of from about 20° C. to about 150° C., in someembodiments from about 50° C. to about 140° C., and in some embodiments,from about 80° C. to about 130° C.

G. Other Components

If desired, the capacitor may also contain other layers as is known inthe art. In certain embodiments, for instance, a carbon layer (e.g.,graphite) may be positioned between the solid electrolyte and the silverlayer that can help further limit contact of the silver layer with thesolid electrolyte. In addition, a pre-coat layer may also be employedthat overlies the dielectric and includes an organometallic compound.

II. Terminations

Once formed, the capacitor element may be provided with terminations,particularly when employed in surface mounting applications. Forexample, the capacitor may contain an anode termination to which ananode lead of the capacitor element is electrically connected and acathode termination to which the cathode of the capacitor element iselectrically connected. Any conductive material may be employed to formthe terminations, such as a conductive metal (e.g., copper, nickel,silver, nickel, zinc, tin, palladium, lead, copper, aluminum,molybdenum, titanium, iron, zirconium, magnesium, and alloys thereof).Particularly suitable conductive metals include, for instance, copper,copper alloys (e.g., copper-zirconium, copper-magnesium, copper-zinc, orcopper-iron), nickel, and nickel alloys (e.g., nickel-iron). Thethickness of the terminations is generally selected to minimize thethickness of the capacitor. For instance, the thickness of theterminations may range from about 0.05 to about 1 millimeter, in someembodiments from about 0.05 to about 0.5 millimeters, and from about0.07 to about 0.2 millimeters. One exemplary conductive material is acopper-iron alloy metal plate available from Wieland (Germany). Ifdesired, the surface of the terminations may be electroplated withnickel, silver, gold, tin, etc. as is known in the art to ensure thatthe final part is mountable to the circuit board. In one particularembodiment, both surfaces of the terminations are plated with nickel andsilver flashes, respectively, while the mounting surface is also platedwith a tin solder layer.

The terminations may be connected to the capacitor element using anytechnique known in the art. In one embodiment, for example, a lead framemay be provided that defines the cathode termination and anodetermination. To attach the electrolytic capacitor element to the leadframe, a conductive adhesive may initially be applied to a surface ofthe cathode termination. The conductive adhesive may include, forinstance, conductive metal particles contained with a resin composition.The metal particles may be silver, copper, gold, platinum, nickel, zinc,bismuth, etc. The resin composition may include a thermoset resin (e.g.,epoxy resin), curing agent (e.g., acid anhydride), and coupling agent(e.g., silane coupling agents). Suitable conductive adhesives may bedescribed in U.S.

Patent Application Publication No. 2006/0038304 to Osako, et al. Any ofa variety of techniques may be used to apply the conductive adhesive tothe cathode termination. Printing techniques, for instance, may beemployed due to their practical and cost-saving benefits. The anode leadmay also be electrically connected to the anode termination using anytechnique known in the art, such as mechanical welding, laser welding,conductive adhesives, etc. Upon electrically connecting the anode leadto the anode termination, the conductive adhesive may then be cured toensure that the electrolytic capacitor element is adequately adhered tothe cathode termination.

III. Housing

The capacitor element may be incorporated within a housing in variousways. In certain embodiments, for instance, the capacitor element may beenclosed within a case, which may then be filled with a resinousmaterial, such as a thermoset resin (e.g., epoxy resin) that can becured to form a hardened housing. The resinous material may surround andencapsulate the capacitor element so that at least a portion of theanode and cathode terminations are exposed for mounting onto a circuitboard. When encapsulated in this manner, the capacitor element andresinous material form an integral capacitor.

Of course, in alternative embodiments, it may be desirable to enclosethe capacitor element within a housing that remains separate anddistinct. In this manner, the atmosphere of the housing can beselectively controlled so that it is dry, which limits the degree ofmoisture that can contact the capacitor element. For example, themoisture content of the atmosphere (expressed in terms of relativehumidity) may be about 10% or less, in some embodiments about 5% orless, in some embodiments about 3% or less, and in some embodiments,from about 0.001 to about 1%. For example, the atmosphere may be gaseousand contain at least one inert gas, such as nitrogen, helium, argon,xenon, neon, krypton, radon, and so forth, as well as mixtures thereof.Typically, inert gases constitute the majority of the atmosphere withinthe housing, such as from about 50 wt. % to 100 wt. %, in someembodiments from about 75 wt. % to 100 wt. %, and in some embodiments,from about 90 wt. % to about 99 wt. % of the atmosphere. If desired, arelatively small amount of non-inert gases may also be employed, such ascarbon dioxide, oxygen, water vapor, etc. In such cases, however, thenon-inert gases typically constitute 15 wt. % or less, in someembodiments 10 wt. % or less, in some embodiments about 5 wt. % or less,in some embodiments about 1 wt. % or less, and in some embodiments, fromabout 0.01 wt. % to about 1 wt. % of the atmosphere within the housing.

Any of a variety of different materials may be used to form the housing,such as metals, plastics, ceramics, and so forth. In one embodiment, forexample, the housing includes one or more layers of a metal, such astantalum, niobium, aluminum, nickel, hafnium, titanium, copper, silver,steel (e.g., stainless), alloys thereof (e.g., electrically conductiveoxides), composites thereof (e.g., metal coated with electricallyconductive oxide), and so forth. In another embodiment, the housing mayinclude one or more layers of a ceramic material, such as aluminumnitride, aluminum oxide, silicon oxide, magnesium oxide, calcium oxide,glass, etc., as well as combinations thereof.

The housing may have any desired shape, such as cylindrical, D-shaped,rectangular, triangular, prismatic, etc. Referring to FIG. 1, forexample, one embodiment of a capacitor 100 is shown that contains ahousing 122 and a capacitor element 120. In this particular embodiment,the housing 122 is generally rectangular. Typically, the housing and thecapacitor element have the same or similar shape so that the capacitorelement can be readily accommodated within the interior cavity. In theillustrated embodiment, for example, both the capacitor element 120 andthe housing 122 have a generally rectangular shape.

If desired, the capacitor of the present invention may exhibit arelatively high volumetric efficiency. To facilitate such highefficiency, the capacitor element typically occupies a substantialportion of the volume of an interior cavity of the housing. For example,the capacitor element may occupy about 30 vol. % or more, in someembodiments about 50 vol. % or more, in some embodiments about 60 vol. %or more, in some embodiments about 70 vol. % or more, in someembodiments from about 80 vol. % to about 98 vol. %, and in someembodiments, from about 85 vol. % to 97 vol. % of the interior cavity ofthe housing. To this end, the difference between the dimensions of thecapacitor element and those of the interior cavity defined by thehousing are typically relatively small.

Referring to FIG. 1, for example, the capacitor element 120 may have alength (excluding the length of the anode lead 6) that is relativelysimilar to the length of an interior cavity 126 defined by the housing122. For example, the ratio of the length of the anode to the length ofthe interior cavity ranges from about 0.40 to 1.00, in some embodimentsfrom about 0.50 to about 0.99, in some embodiments from about 0.60 toabout 0.99, and in some embodiments, from about 0.70 to about 0.98. Thecapacitor element 120 may have a length of from about 5 to about 10millimeters, and the interior cavity 126 may have a length of from about6 to about 15 millimeters. Similarly, the ratio of the height of thecapacitor element 120 (in the −z direction) to the height of theinterior cavity 126 may range from about 0.40 to 1.00, in someembodiments from about 0.50 to about 0.99, in some embodiments fromabout 0.60 to about 0.99, and in some embodiments, from about 0.70 toabout 0.98. The ratio of the width of the capacitor element 120 (in the−x direction) to the width of the interior cavity 126 may also rangefrom about 0.50 to 1.00, in some embodiments from about 0.60 to about0.99, in some embodiments from about 0.70 to about 0.99, in someembodiments from about 0.80 to about 0.98, and in some embodiments, fromabout 0.85 to about 0.95. For example, the width of the capacitorelement 120 may be from about 2 to about 7 millimeters and the width ofthe interior cavity 126 may be from about 3 to about 10 millimeters, andthe height of the capacitor element 120 may be from about 0.5 to about 2millimeters and the width of the interior cavity 126 may be from about0.7 to about 6 millimeters.

Although by no means required, the capacitor element may be attached tothe housing in such a manner that an anode termination and cathodetermination are formed external to the housing for subsequentintegration into a circuit. The particular configuration of theterminations may depend on the intended application. In one embodiment,for example, the capacitor may be formed so that it is surfacemountable, and yet still mechanically robust. For example, the anodelead may be electrically connected to external, surface mountable anodeand cathode terminations (e.g., pads, sheets, plates, frames, etc.).Such terminations may extend through the housing to connect with thecapacitor. The thickness or height of the terminations is generallyselected to minimize the thickness of the capacitor. For instance, thethickness of the terminations may range from about 0.05 to about 1millimeter, in some embodiments from about 0.05 to about 0.5millimeters, and from about 0.1 to about 0.2 millimeters. If desired,the surface of the terminations may be electroplated with nickel,silver, gold, tin, etc. as is known in the art to ensure that the finalpart is mountable to the circuit board. In one particular embodiment,the termination(s) are deposited with nickel and silver flashes,respectively, and the mounting surface is also plated with a tin solderlayer. In another embodiment, the termination(s) are deposited with thinouter metal layers (e.g., gold) onto a base metal layer (e.g., copperalloy) to further increase conductivity.

In certain embodiments, connective members may be employed within theinterior cavity of the housing to facilitate connection to theterminations in a mechanically stable manner. For example, referringagain to FIG. 1, the capacitor 100 may include a connection member 162that is formed from a first portion 167 and a second portion 165. Theconnection member 162 may be formed from conductive materials similar tothe external terminations. The first portion 167 and second portion 165may be integral or separate pieces that are connected together, eitherdirectly or via an additional conductive element (e.g., metal). In theillustrated embodiment, the second portion 165 is provided in a planethat is generally parallel to a lateral direction in which the lead 6extends (e.g., −y direction). The first portion 167 is “upstanding” inthe sense that it is provided in a plane that is generally perpendicularthe lateral direction in which the lead 6 extends. In this manner, thefirst portion 167 can limit movement of the lead 6 in the horizontaldirection to enhance surface contact and mechanical stability duringuse. If desired, an insulative material 7 (e.g., Teflon™ washer) may beemployed around the lead 6.

The first portion 167 may possess a mounting region (not shown) that isconnected to the anode lead 6. The region may have a “U-shape” forfurther enhancing surface contact and mechanical stability of the lead6. Connection of the region to the lead 6 may be accomplished using anyof a variety of known techniques, such as welding, laser welding,conductive adhesives, etc. In one particular embodiment, for example,the region is laser welded to the anode lead 6. Regardless of thetechnique chosen, however, the first portion 167 can hold the anode lead6 in substantial horizontal alignment to further enhance the dimensionalstability of the capacitor 100.

Referring again to FIG. 1, one embodiment of the present invention isshown in which the connective member 162 and capacitor element 120 areconnected to the housing 122 through anode and cathode terminations 127and 129, respectively. More specifically, the housing 122 of thisembodiment includes an outer wall 123 and two opposing sidewalls 124between which a cavity 126 is formed that includes the capacitor element120. The outer wall 123 and sidewalls 124 may be formed from one or morelayers of a metal, plastic, or ceramic material such as described above.In this particular embodiment, the anode termination 127 contains afirst region 127 a that is positioned within the housing 122 andelectrically connected to the connection member 162 and a second region127 b that is positioned external to the housing 122 and provides amounting surface 201. Likewise, the cathode termination 129 contains afirst region 129 a that is positioned within the housing 122 andelectrically connected to the solid electrolyte of the capacitor element120 and a second region 129 b that is positioned external to the housing122 and provides a mounting surface 203. It should be understood thatthe entire portion of such regions need not be positioned within orexternal to the housing.

In the illustrated embodiment, a conductive trace 127 c extends in theouter wall 123 of the housing to connect the first region 127 a andsecond region 127 b. Similarly, a conductive trace 129 c extends in theouter wall 123 of the housing to connect the first region 127 a andsecond region 127 b. The conductive traces and/or regions of theterminations may be separate or integral. In addition to extendingthrough the outer wall of the housing, the traces may also be positionedat other locations, such as external to the outer wall. Of course, thepresent invention is by no means limited to the use of conductive tracesfor forming the desired terminations.

Regardless of the particular configuration employed, connection of theterminations 127 and 129 to the capacitor element 120 may be made usingany known technique, such as welding, laser welding, conductiveadhesives, etc. In one particular embodiment, for example, a conductiveadhesive 131 is used to connect the second portion 165 of the connectionmember 162 to the anode termination 127. Likewise, a conductive adhesive133 is used to connect the cathode of the capacitor element 120 to thecathode termination 129.

Optionally, a polymeric restraint may also be disposed in contact withone or more surfaces of the capacitor element, such as the rear surface,front surface, upper surface, lower surface, side surface(s), or anycombination thereof. The polymeric restraint can reduce the likelihoodof delamination by the capacitor element from the housing. In thisregard, the polymeric restraint may possess a certain degree of strengththat allows it to retain the capacitor element in a relatively fixedpositioned even when it is subjected to vibrational forces, yet is notso strong that it cracks. For example, the restraint may possess atensile strength of from about 1 to about 150 Megapascals (“MPa”), insome embodiments from about 2 to about 100 MPa, in some embodiments fromabout 10 to about 80 MPa, and in some embodiments, from about 20 toabout 70 MPa, measured at a temperature of about 25° C. It is normallydesired that the restraint is not electrically conductive. Referringagain to FIG. 1, for instance, one embodiment is shown in which a singlepolymeric restraint 197 is disposed in contact with an upper surface 181and rear surface 177 of the capacitor element 120. While a singlerestraint is shown in FIG. 1, it should be understood that separaterestraints may be employed to accomplish the same function. In fact,more generally, any number of polymeric restraints may be employed tocontact any desired surface of the capacitor element. When multiplerestraints are employed, they may be in contact with each other orremain physically separated. For example, in one embodiment, a secondpolymeric restraint (not shown) may be employed that contacts the uppersurface 181 and front surface 179 of the capacitor element 120. Thefirst polymeric restraint 197 and the second polymeric restraint (notshown) may or may not be in contact with each other. In yet anotherembodiment, a polymeric restraint may also contact a lower surface 183and/or side surface(s) of the capacitor element 120, either inconjunction with or in lieu of other surfaces.

Regardless of how it is applied, it is typically desired that thepolymeric restraint is also in contact with at least one surface of thehousing to help further mechanically stabilize the capacitor elementagainst possible delamination. For example, the restraint may be incontact with an interior surface of one or more sidewall(s), outer wall,lid, etc. In FIG. 1, for example, the polymeric restraint 197 is incontact with an interior surface 107 of sidewall 124 and an interiorsurface 109 of outer wall 123. While in contact with the housing, it isnevertheless desired that at least a portion of the cavity defined bythe housing remains unoccupied to allow for the inert gas to flowthrough the cavity and limit contact of the solid electrolyte withoxygen. For example, at least about 5% of the cavity volume typicallyremains unoccupied by the capacitor element and polymer restraint, andin some embodiments, from about 10% to about 50% of the cavity volume.

Once connected in the desired manner, the resulting package ishermetically sealed as described above. Referring again to FIG. 1, forinstance, the housing 122 may also include a lid 125 that is placed onan upper surface of side walls 124 after the capacitor element 120 andthe polymer restraint 197 are positioned within the housing 122. The lid125 may be formed from a ceramic, metal (e.g., iron, copper, nickel,cobalt, etc., as well as alloys thereof), plastic, and so forth. Ifdesired, a sealing member 187 may be disposed between the lid 125 andthe side walls 124 to help provide a good seal. In one embodiment, forexample, the sealing member may include a glass-to-metal seal, Kovar®ring (Goodfellow Camridge, Ltd.), etc. The height of the side walls 124is generally such that the lid 125 does not contact any surface of thecapacitor element 120 so that it is not contaminated. The polymericrestraint 197 may or may not contact the lid 125. When placed in thedesired position, the lid 125 is hermetically sealed to the sidewalls124 using known techniques, such as welding (e.g., resistance welding,laser welding, etc.), soldering, etc. Hermetic sealing generally occursin the presence of inert gases as described above so that the resultingassembly is substantially free of reactive gases, such as oxygen orwater vapor.

It should be understood that the embodiments described are onlyexemplary, and that various other configurations may be employed in thepresent invention for hermetically sealing a capacitor element within ahousing. Referring to FIG. 2, for instance, another embodiment of acapacitor 200 is shown that employs a housing 222 that includes an outerwall 123 and a lid 225 between which a cavity 126 is formed thatincludes the capacitor element 120 and polymeric restraint 197. The lid225 includes an outer wall 223 that is integral with at least onesidewall 224. In the illustrated embodiment, for example, two opposingsidewalls 224 are shown in cross-section. The outer walls 223 and 123both extend in a lateral direction (−y direction) and are generallyparallel with each other and to the lateral direction of the anode lead6. The sidewall 224 extends from the outer wall 223 in a longitudinaldirection that is generally perpendicular to the outer wall 123. Adistal end 500 of the lid 225 is defined by the outer wall 223 and aproximal end 501 is defined by a lip 253 of the sidewall 224.

The lip 253 extends from the sidewall 224 in the lateral direction,which may be generally parallel to the lateral direction of the outerwall 123. The angle between the sidewall 224 and the lip 253 may vary,but is typically from about 60° to about 120°, in some embodiments fromabout 70° to about 110°, and in some embodiments, from about 80° toabout 100° (e.g., about 90°). The lip 253 also defines a peripheral edge251, which may be generally perpendicular to the lateral direction inwhich the lip 253 and outer wall 123 extend. The peripheral edge 251 islocated beyond the outer periphery of the sidewall 224 and may begenerally coplanar with an edge 151 of the outer wall 123. The lip 253may be sealed to the outer wall 123 using any known technique, such aswelding (e.g., resistance or laser), soldering, glue, etc. For example,in the illustrated embodiment, a sealing member 287 is employed (e.g.,glass-to-metal seal, Kovar® ring, etc.) between the components tofacilitate their attachment. Regardless, the use of a lip describedabove can enable a more stable connection between the components andimprove the seal and mechanical stability of the capacitor.

Still other possible housing configurations may be employed in thepresent invention. For example, FIG. 3 shows a capacitor 300 having ahousing configuration similar to that of FIG. 2, except that terminalpins 327 b and 329 b are employed as the external terminations for theanode and cathode, respectively. More particularly, the terminal pin 327a extends through a trace 327 c formed in the outer wall 323 and isconnected to the anode lead 6 using known techniques (e.g., welding). Anadditional section 327 a may be employed to secure the pin 327 b.Likewise, the terminal pin 329 b extends through a trace 329 c formed inthe outer wall 323 and is connected to the cathode via a conductiveadhesive 133 as described above.

The embodiments shown in FIGS. 1-3 are discussed herein in terms of onlya single capacitor element. It should also be understood, however, thatmultiple capacitor elements may also be hermetically sealed within ahousing. The multiple capacitor elements may be attached to the housingusing any of a variety of different techniques. Referring to FIG. 4, forexample one particular embodiment of a capacitor 400 that contains twocapacitor elements is shown and will now be described in more detail.More particularly, the capacitor 400 includes a first capacitor element420 a in electrical communication with a second capacitor element 420 b.In this embodiment, the capacitor elements are aligned so that theirmajor surfaces are in a horizontal configuration. That is, a majorsurface of the capacitor element 420 a defined by its width (−xdirection) and length (−y direction) is positioned adjacent to acorresponding major surface of the capacitor element 420 b. Thus, themajor surfaces are generally coplanar. Alternatively, the capacitorelements may be arranged so that their major surfaces are not coplanar,but perpendicular to each other in a certain direction, such as the −zdirection or the −x direction. Of course, the capacitor elements neednot extend in the same direction.

The capacitor elements 420 a and 420 b are positioned within a housing422 that contains an outer wall 423 and sidewalls 424 and 425 thattogether define a cavity 426. Although not shown, a lid may be employedthat covers the upper surfaces of the sidewalls 424 and 425 and sealsthe assembly 400 as described above. Optionally, a polymeric restraintmay also be employed to help limit the vibration of the capacitorelements. In FIG. 4, for example, separate polymer restraints 497 a and497 b are positioned adjacent to and in contact with the capacitorelements 420 a and 420 b, respectively. The polymer restraints 497 a and497 b may be positioned in a variety of different locations. Further,one of the restraints may be eliminated, or additional restraints may beemployed. In certain embodiments, for example, it may be desired toemploy a polymeric restraint between the capacitor elements to furtherimprove mechanical stability.

In addition to the capacitor elements, the capacitor also contains ananode termination to which anode leads of respective capacitor elementsare electrically connected and a cathode termination to which thecathodes of respective capacitor elements are electrically connected.Referring again to FIG. 4, for example, the capacitor elements are shownconnected in parallel to a common cathode termination 429. In thisparticular embodiment, the cathode termination 429 is initially providedin a plane that is generally parallel to the bottom surface of thecapacitor elements and may be in electrical contact with conductivetraces (not shown). The capacitor 400 also includes connective members427 and 527 that are connected to anode leads 407 a and 407 b,respectively, of the capacitor elements 420 a and 420 b. Moreparticularly, the connective member 427 contains an upstanding portion465 and a planar portion 463 that is in connection with an anodetermination (not shown). Likewise, the connective 527 contains anupstanding portion 565 and a planar portion 563 that is in connectionwith an anode termination (not shown). Of course, it should beunderstood that a wide variety of other types of connection mechanismsmay also be employed.

The present invention may be better understood with reference to thefollowing examples.

Test Procedures Capacitance

The capacitance was measured using a Keithley 3330 Precision LCZ meterwith Kelvin Leads with 2.2 volt DC bias and a 0.5 volt peak to peaksinusoidal signal. The operating frequency was 120 Hz and thetemperature may be 23° C. t 2° C.

Breakdown Voltage

The breakdown voltage was measured using Keithley 2400 SourceMeter atthe temperature 23° C. t 2° C. An individual capacitor is charged withconstant current determined by the equation:

Current (A)=Nominal Capacitance (F)×dU/dt,

where dU/dt represents voltage slope typically set to 10 V/s. Voltage ismeasured during charging and when applied voltage decreases more than10%, the maximum achieved voltage value is recorded as breakdownvoltage.

Equivalent Series Resistance (ESR)

Equivalence series resistance may be measured using a Keithley 3330Precision LCZ meter with Kelvin Leads 2.2 volt DC bias and a 0.5 voltpeak to peak sinusoidal signal. The operating frequency was 100 kHz andthe temperature was 23° C. t 2° C.

Dissipation Factor

The dissipation factor may be measured using a Keithley 3330 PrecisionLCZ meter with Kelvin Leads with 2.2 volt DC bias and a 0.5 volt peak topeak sinusoidal signal. The operating frequency may be 120 Hz and thetemperature may be 23° C.±2° C.

Leakage Current

Leakage current may be measured using a leakage test meter at atemperature of 23° C.+2° C. and at the rated voltage after a minimum of60 seconds.

Surge Voltage Testing

Surge voltage testing may be conducted (10-25 parts) at a temperature of85° C.±3° C. and the rated voltage multiple by 1.3 (e.g., 45.5V). Theresistance used in test circuit may be 33 ohms. Each cycle consists of30 seconds surge voltage application followed by a 30 second dischargeperiod. Tested samples are dried before testing at 125° C. for at least12 hours. The capacitance may be measured at each 1,000 pulse cycles upto 5,000 pulses after the recovery time.

Dielectric Thickness

The dielectric thickness may be measured using a Zeiss Sigma FESEM at20,000× to 50,000× magnification. Samples may be prepared by cutting afinished part in plane perpendicular to the longest dimension of thefinished part. A thickness measurement may be performed at sites wherethe cut was perpendicular direction through the dielectric layer.

Example 1

40,000 μFV/g tantalum powder was used to form anode samples. Each anodesample was embedded with a tantalum wire, pressed to a density of 5.1g/cm³ and sintered at 1440° C. The resulting pellets had a size of5.60×3.65×0.90 mm. The pellets were anodized to 81.0 volts inwater/phosphoric acid electrolyte with a conductivity of 8.6 mS at atemperature of 40° C. to form the dielectric layer. The pellets wereanodized again to 150 volts in a water/boric acid/disodium tetraboratewith a conductivity of 2.0 mS at a temperature of 30° C. for 15 secondsto form a thicker oxide layer built up on the outside. A conductivepolymer coating was formed by dipping the anodes into a solution ofpoly(4-(2,3-dihydrothieno-[3,4-b][1,4]dioxin-2-ylmethoxy)-2-butane-sulphonicacid. Upon coating, the parts were dried at 125° C. for 15 minutes. Thisprocess was repeated 7 times. Thereafter, the parts were dipped into adispersed poly(3,4-ethylenedioxythiophene) having a solids content 1.1%and viscosity 20 mPa·s (Clevios™ K, Heraeus). Upon coating, the partswere dried at 125° C. for 15 minutes. This process was repeated 8 times.Thereafter, the parts were dipped into a dispersedpoly(3,4-ethylenedioxythiophene) having a solids content 2.0% andviscosity 20 mPa·s (Clevios™ K, Heraeus). Upon coating, the parts weredried at 125° C. for 15 minutes. This process was repeated 3 times.Thereafter, the parts were dipped into a dispersedpoly(3,4-ethylenedioxythiophene) having a solids content of 2% andviscosity 160 mPa·s (Clevios™ K, Heraeus). Upon coating, the parts weredried at 125° C. for 15 minutes. This process was repeated 14 times. Theparts were then dipped into a graphite dispersion and dried. Finally,the parts were dipped into a silver dispersion and dried. Multiple parts(360) of 47F/35V capacitors were made in this manner and encapsulated ina silica resin.

Example 2

Capacitors were formed in the manner described in Example 1, except thatfour pre-coat layers of organometallic compound were used that containeda solution of (3-aminopropyl)trimethoxysilane in ethanol (1.0%) and adifferent conductive polymer coating was used. Namely, the conductivepolymer coating was formed by dipping the anodes into a solution ofpoly(4-(2,3-dihydrothieno-[3,4-b][1,4]dioxin-2-ylmethoxy)-2-butane-sulphonicacid. Upon coating, the parts were dried at 125° C. for 15 minutes. Thisprocess was repeated 6 times. Thereafter, the parts were dipped into adispersed poly(3,4-ethylenedioxythiophene) having a solids content 1.1%and viscosity 20 mPa·s (Clevios™ K, Heraeus). Upon coating, the partswere dried at 125° C. for 15 minutes. This process was repeated 8 times.Thereafter, the parts were dipped into a dispersedpoly(3,4-ethylenedioxythiophene) having a solids content 2.0% andviscosity 20 mPa·s (Clevios™ K, Heraeus). Upon coating, the parts weredried at 125° C. for 15 minutes. This process was repeated 3 times.Thereafter, the parts were dipped into a dispersedpoly(3,4-ethylenedioxythiophene) having a solids content of 2% andviscosity 160 mPa·s (Clevios™ K, Heraeus). Upon coating, the parts weredried at 125° C. for 15 minutes. This process was repeated 14 times. Theparts were then dipped into a graphite dispersion and dried. Finally,the parts were dipped into a silver dispersion and dried. Multiple parts(360) of 47F/35V capacitors were made in this manner and encapsulated ina silica resin.

The median results of capacitance after surge voltage testing are setforth below in Table 1.

TABLE 1 Surge Voltage Testing Results Median Ratio of CapacitanceCapacitance After Surge Testing to Cycles (μF) Initial CapacitanceExample 1 0 45.63 — 1,000 41.30 0.90 2,000 38.69 0.85 3,000 37.25 0.824,000 35.71 0.78 5,000 34.42 0.75 Example 2 0 44.11 — 1,000 43.32 0.982,000 43.03 0.98 3,000 42.62 0.97 4,000 42.34 0.96 5,000 41.58 0.94

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims.

What is claimed is:
 1. A solid electrolytic capacitor comprising a capacitor element, wherein the capacitor element comprises: an anode body; a dielectric that overlies the anode body; a pre-coat that overlies the anode body, wherein the pre-coat is formed from an organometallic compound; and a solid electrolyte that overlies the dielectric, wherein the solid electrolyte includes an intrinsically conductive polymer containing repeating thiophene units of the following general formula (I):

wherein, a is from 0 to 10; b is from 1 to 18; R is an optionally substituted C₁-C₆ linear or branched alkyl group or a halogen atom; and M is a hydrogen atom, an alkali metal, NH(R¹)₃, or HNC₅H₅, wherein R¹ is each independently a hydrogen atom or an optionally substituted C₁-C₆ alkyl group.
 2. The solid electrolytic capacitor of claim 1, wherein a is 1 and b is 3 or
 4. 3. The solid electrolytic capacitor of claim 1, wherein R is methyl.
 4. The solid electrolytic capacitor of claim 1, wherein M is an alkali metal.
 5. The solid electrolytic capacitor of claim 1, wherein the thiophene repeating units are formed from sodium 3-[(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-ethyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-propyl-1-propane-sulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-butyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-pentyl-1-propane-sulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-hexyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-isopropyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-isobutyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-isopentyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-fluoro-1-propanesulfonate, potassium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate, 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonic acid, ammonium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propane-sulfonate, triethylammonium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate, or a combination thereof.
 6. The solid electrolytic capacitor of claim 1, wherein the polymer has a specific conductivity of about 20 S/cm or more.
 7. The solid electrolytic capacitor of claim 1, wherein the solid electrolyte contains at least one inner layer that includes the intrinsically conductive polymer.
 8. The solid electrolytic capacitor of claim 7, wherein the inner layer is generally free of an extrinsically conductive polymer.
 9. The solid electrolytic capacitor of claim 1, wherein the solid electrolyte contains at least outer layer.
 10. The solid electrolytic capacitor of claim 9, wherein the outer layer is formed from particles that contain a polymeric counterion and an extrinsically conductive polymer.
 11. The solid electrolytic capacitor of claim 9, wherein the outer layer contains a hydroxyl-functional nonionic polymer.
 12. The solid electrolytic capacitor of claim 1, wherein the organometallic compound is a monoaminofunctional silane having the following general formula (II):

wherein, R₁, R₂, and R₃ are independently alkyl, alkenyl, aryl, heteroaryl, cycloalkyl, heterocyclyl, halo, haloalkyl, or hydroxyalkyl; R₄ and R₅ are independently hydrogen, alkyl, independently alkyl, alkenyl, aryl, heteroaryl, cycloalkyl, heterocyclyl, halo, haloalkyl, hydroxyalkyl, or alternatively N, R₄, and R₅ together with one or more additional atoms form a ring structure; and Z is an organic group.
 13. The solid electrolytic capacitor of claim 12, wherein the monoaminofunctional silane is a primary amine.
 14. The solid electrolytic capacitor of claim 13, wherein the primary amine is 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 4-aminobutyltriethoxysilane, m-aminophenyltrimethoxysilane, p-aminophenyltrimethoxysilane, aminophenyltrimethoxysilane, 3-aminopropyltris(methoxy-ethoxy)silane, 11-aminoundecyltriethoxysilane, 2(4-pyridylethyl)triethoxysilane, 2-(trimethoxysilylethyl)pyridine, N-(3-trimethoxysilylpropyl)pyrrole, 3-(m-aminophenoxypropyltrimethoxysilane, aminopropylsilanetriol, 3-aminopropylmethyldiethoxysilane, 3-aminopropyldiisopropylethoxysilane, 3-aminopropyldimethylethoxysilane, or a combination thereof.
 15. The solid electrolytic capacitor of claim 12, wherein the monoaminofunctional silane is a secondary amine.
 16. The solid electrolytic capacitor of claim 15, wherein the secondary amine is N-butylaminopropyltrimethoxy silane, N-ethylaminoisobutyltrimethoxysilane, n-methylaminopropyltrimethoxysilane, N-phenylaminopropyltrimethoxy silane, 3-(N-allylamino)propyltrimethoxysilane, cyclohexylaminomethyl)triethoxysilane, N-cyclohexylaminopropyltrimethoxysilane, N-ethylaminoisobutylmethyldiethoxysilane, (phenylaminoethyl)methyl-diethoxysilane, N-phenylaminomethytrimethoxysilane, N-methylaminopropylmethyl-dimethoxysilane, or a combination thereof.
 17. The solid electrolytic capacitor of claim 1, wherein the organometallic compound is a diaminofunctional silane having the following general formula (III):

wherein, R₁, R₂, and R₃ are independently alkyl, alkenyl, aryl, heteroaryl, cycloalkyl, heterocyclyl, halo, haloalkyl, or hydroxyalkyl; and Z₁ and Z₂ are independently an organic group.
 18. The solid electrolytic capacitor of claim 17, wherein the diaminofunctional silane is N-(2-aminoethyl)-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(6-aminohexyl)aminomethyltriethoxysilane, N-(6-aminohexyl)aminopropyltrimethoxysilane, N-(2-aminoethyl)-11-aminoundecyltrimethoxysilane), (aminoethylaminomethyl)-phenethyltrimethoxysilane, N-3-[(amino(polypropylenoxy)]-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylsilanetriol, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminoisobutylmethyldimethoxysilane, (aminoethylamino)-3-isobutyldimethylmethoxysilane, or a combination thereof.
 19. The solid electrolytic capacitor of claim 1, further comprising an external polymer coating that overlies the solid electrolyte and contains conductive polymer particles.
 20. The solid electrolytic capacitor of claim 19, wherein the external polymer coating further comprises a crosslinking agent.
 21. The solid electrolytic capacitor of claim 1, wherein the anode body is a sintered pellet.
 22. The solid electrolytic capacitor of claim 1, wherein the anode body is a foil.
 23. The solid electrolytic capacitor of claim 1, further comprising a housing within which the capacitor element is enclosed.
 24. The solid electrolytic capacitor of claim 1, wherein the capacitor element further comprises a cathode coating that contains a metal particle layer that overlies the solid electrolyte, wherein the metal particle layer includes a plurality of conductive metal particles.
 25. The solid electrolytic capacitor of claim 1, wherein the capacitor exhibits a breakdown voltage of about 55 volts or more.
 26. The solid electrolytic capacitor of claim 1, wherein the capacitor exhibits a charge-discharge capacitance after being subjected to 5,000 cycles of a surge voltage and an initial capacitance prior to being subjected to the 5,000 cycles of the surge voltage, wherein the ratio of the charge-discharge capacitance to the initial capacitance is from about 0.9 to
 1. 